Vehicle traction control system

Abstract

In a traction control system for a vehicle which controls the traction of the driven wheels according to the slip ratio of the driven wheels obtained as a relationship between the vehicle speed and the speed of the driven wheels, the vehicle speed is obtained from the speed of the non-driven wheels. Normally, the average value of the speeds of the non-driven wheels is used as the basis for computing the vehicle speed, but when one of the non-driven wheels is likely to be lifted from the road surface due to the turning maneuver of the vehicle, the speed of one of the non-driven wheels which is higher than that of the other non-driven wheel and is therefore likely to be in contact with the road surface is used for fining the vehicle speed. Thus, the vehicle speed is simply obtained from the speed of the non-driven wheels, but the traction control can be reliably carried out according to a correctly obtained vehicle speed.

We claim: 
     
       1. A traction control system for a vehicle having a pair of driven wheels, and a pair of non-driven wheels, comprising: driven wheel speed detecting means for detecting speeds of said driven wheels;   non-driven wheel speed detecting means for detecting speeds of said non-driven wheels;   vehicle speed determining means for determining a vehicle speed from speeds detected by said non-driven wheel speed detecting means;   slip detecting means for detecting a measure of the slipping of said driven wheels by comparing speeds detected by said driven wheel speed detecting means with said vehicle speed determined by said vehicle speed determining means;   traction control means for controlling traction of said vehicle wheels according to said measure of the slipping of said driven wheels detected by said slip detecting means; and   wheel lift detecting means for detecting a substantial lifting of one of said non-driven wheels from a road surface,   wherein when said wheel lift detecting means has detected a substantial lifting of one of said non-driven wheels from the road surface, said vehicle speed determining means determines said vehicle speed solely from the speed of the other of said non-driven wheels.   
     
     
       2. A vehicle traction control system according to claim 1, wherein said vehicle speed determining means determines said vehicle speed from an average value of the speeds of said non-driven wheels when said wheel lift detecting means has not detected a substantial lifting of either one of said non-driven wheels from the road surface, and from the speed of one of said non-driven wheels when said wheel lift detecting means has detected a substantial lifting of the other of said non-driven wheels from the road surface. 
     
     
       3. A vehicle traction control system according to claim 1, wherein said wheel lift detecting means comprises a lateral acceleration sensor, and detects a substantial lifting of one of said non-driven wheels by detecting a lateral acceleration exceeding a certain threshold value. 
     
     
       4. A vehicle traction control system according to claim 3, wherein said threshold value is dependent on a value indicative of a vehicle speed. 
     
     
       5. A vehicle traction control system according to claim 1, wherein said wheel lift detecting means comprises means for computing a difference between the speeds of said non-driven wheels, and detects a substantial lifting of one of said non-driven wheels by detecting said difference exceeding a certain threshold value. 
     
     
       6. A vehicle traction control system according to claim 1, wherein said wheel lift detecting means comprises means for computing a difference between the speeds of said driven wheels, and detects a substantial lifting of one of said driven wheels by detecting said difference exceeding a certain threshold value. 
     
     
       7. A vehicle traction control system according to claim 1, wherein said wheel lift detecting means comprises a steering angle sensor, and detects a substantial lifting of one of said non-driven wheels by detecting a steering angle exceeding a certain threshold value which is given as a mathematical function of said vehicle speed. 
     
     
       8. A vehicle traction control system according to claim 1, wherein said wheel lift detecting means comprises a vertical load sensor for detecting a vertical load acting on each of said non-driven wheels, and detects a substantial lifting of one of said non-driven wheels by detecting a vertical load exceeding a certain threshold value.